hey wesmkdro, i was wondering this same thing, if i have a batch a nutrients that sits around too long it seems to form something, maybe mold after about 5 days, so i would say the shorter the better
I know that Liquid Karma is bad after 24 hours of sitting mixed but "Boost" by canna has to be used with 7 days, so I would say it is different per product. I usually only let my mixed water sit no longer than 24 hours unless it's for foliar feeding.